Showing papers on "Substituent published in 1977"

Gas phase basicities and relative proton affinities of compounds between water and ammonia from pulsed ion cyclotron resonance thermal equilibriums measurements

Abstract: The pulsed ion cyclotron resonance method for precise determinations of proton transfer equilibrium constants has been applied to 46 carbon, nitrogen, oxygen, phosphorus, sulfur, arsenic, and selenium bases, with duplicating overlapping sequences, to obtain the relative proton affinities of water and ammonia. Where comparison is possible, the results are in generally good accord with those obtained by high-pressure mass spectroscopy. The results provide important new insights into the intrinsic effects of molecular structure on base strengths. Applications of these results to derive other gaseous ion thermochemical data are illustrated. In particular, methyl substituent effects on proton affinities have been extensively evaluated and interpretations are made of the comparisons with corresponding effects of homolytic bond dissociation energies of the conjugate acids of n-bases and with the hydride affinities of substituted methyl cations. Comparisons of the effects of n-alkyl substituents on the proton affinities of water and alcohols with carboxylic acids and their esters indicate that protonation is thermodynamically favored in the gas phase at the carbonyl oxygen of the latter. Large effects of polar electronegative substituents have been observed for various oxygen and nitrogen bases. An evaluation of entropy effects in gas phase proton transfer equilibria shows such effects to bemore » generally small for simple bases and approximately equal to entropy effects expected for changes in molecular rotational symmetry numbers. Finally, the present result provides the basis for evaluations of absolute proton affinities and of relative ion solvation energies.« less

The semiempirical derivation of 13C nuclear magnetic resonance chemical shifts. Hydrocarbons, alcohols, amines, ketones, and olefins

Abstract: Substituent parameters were derived for the semiempirical determination of 13C chemical shifts in saturated hydrocarbons, alcohols, amines, ketones, and olefins. The olefin parameters are valid for six-membered rings and the remaining parameters for six-membered rings in chair conformations. The use of these parameters for the calculation of carbon resonances is illustrated with a number of examples.

Selective production of para dialkyl substituted benzenes

Abstract: A catalytic process is provided for the selective production of para dialkyl substituted benzenes containing alkyl groups of 1 to 4 carbon atoms, typified by para-xylene, by contacting, under conversion conditions, a hydrocarbon precursor selected from the group consisting of mono alkyl-substituted benzenes having 1-4 carbon atoms in the alkyl substituent, e.g., toluene, ethyl benzene, propyl benzene, or butyl benzene; a C2 -C15 olefin and a C3 -C60 paraffin, or mixtures thereof including mixtures of benzene with at least one of the aforementioned olefins or paraffins with a zeolite-containing catalyst characterized by a xylene sorption capacity greater than 1 gram/100 grams of zeolite and an ortho xylene sorption time for 30 percent of said capacity of greater than 10 minutes, said sorption capacity and sorption time being measured at 120° C and a xylene pressure of 4.5 ±0.8 mm. of mercury, said catalyst comprising a crystalline aluminosilicate zeolite having a silica to alumina ratio of at least about 12 and a constraint index, as hereinafter defined, within the approximate range of 1 to 12 and recovering from the resulting product mixture, a para dialkyl substituted benzene in an amount greater than the thermodynamic equilibrium concentration thereof in total dialkyl substituted benzenes produced.

Carbon-13 Nuclear Magnetic Resonance Examination of Naphthalene Derivatives. Assignments and Analysis of Substituent Chemical Shifts

Abstract: The natural abundance C NMR spectra of a number of substituted naphthalenes have been obtained and assigned by utilization of some or all of the following criteria: (a) specific H incorporation and spectral consequences thereof, (b) fully proton coupled spectra, (c) fluoro substitution, and (d) approximate additivity of substituent effects on chemical shifts for certain dispositions. For crucial sets of 1-and 2-substituted naphthalenes, spectra have been obtained under dilute conditions in chloroform and acetone, and the substituent chemical shifts have been treated by the dual substituent parameter equation (DSP analysis) to provide further insight into the transmission of substituent effects in the naphthyl system.

Substituent effects on the carbon-13 N.M.R. chemical shifts of side-chain carbons in aromatic systems

Abstract: Carbon-13 chemical shifts have been measured for the side-chain carbon atoms of a number of meta- and para-disubstituted benzenes. The side chains examined were CN, CF3, Ac, CO2Et, Me, OMe and NMe2. The substituent-induced 13C shifts of these side chains were related to Hammett substituent effects by the Dual Substituent Parameter method and showed a widely varying dependence upon the blend of inductive and resonance effects. The transmission of substituent effects through aromatic systems and the factors that influence 13C shifts are discussed.

The eosin-sensitized photooxidation of substituted phenylalanines and tyrosines.

Abstract: — The eosin-sensitized photooxidation of tyrosine and a number of compounds related to tyrosine (substituted phenylalanines) was studied by steady-state kinetic and flash photolysis techniques. In particular, the role of the phenolic group and the amino and carboxyl groups of the alanyl side chain in the photooxidation mechanism was investigated in detail. Several relationships between substrate structure and susceptibility to photooxidation as well as effects of substrate structure on photooxidation mechanisms were found. For example, phenylalanine is not photooxidizable, hut substitution of electron-donating (activating) groups such as-OH (as in tyrosine) or-NH2 (as in p-aminophenylalanine) results in rapidly photooxidized derivatives. However, substituting deactivating groups such as—C1 (as in p-chlorophenylalanine) or weakly activating groups such as - OCH3 (as in 4-methoxyphenylalanine) result in non-photooxidiz-able derivatives. Substitution of additional activating groups to the ring of hydroxy-substituted phenylalanines results in increased rates of photooxidation, whereas additional deactivating groups result in decreased photooxidation rates. The rate-determining step in the photooxidation mechanism is shown to be dependent on the presence and position of an electron-donating substituent on the benzenoid ring. Only minor involvement of the side chain amino and carboxyl groups was found. Both singlet oxygen and hydrogen abstraction mechanisms are involved in the eosin-sensitized photooxidation of hydroxy-substituted phenylalanines (e.g. tyrosine). The hydrogen abstraction mechanism probably predominates at both pH 8 and 11.

Conformational analysis of 2-substituted methylenecyclohexanes and 3-substituted cyclohexenes and the anomeric effect

Abstract: The analysis of the 13C and 1H nuclear magnetic resonance data of 2-substituted methylenecyclohexanes and 3-substituted cyclohexenes demonstrates that a double bond stabilizes the axial conformer for an electronegative substituent. Introduction of a methoxy group on the double bond further increases the relative stability of the axial conformer. These results are interpreted in terms of the 'double bond – no bond' resonance.

Influence of substituent ribose on transition state affinity in reactions catalyzed by adenosine deaminase.

Abstract: Adenosine deaminase from calf intestine hydrolyzes adenine at a limiting rate four orders of magnitude lower than that for adenosine, while Km values for these substrates are about the same (Wolfenden, R., et al. (1969), Biochemistry 8, 2412-2415). Reactivity of 6-substituents, toward nucleophilic displacement, is found to be affected only slightly by removal of ribose as a 9-substituent, in model reactions. Substituent ribose thus appears to stabilize, selectively, the transition state for enzymatic deamination. In contrast with the small influence of substituent ribose on the apparent binding affinity of substrates, removal of substituent ribose from a potential transition state analogue, 1,6-dihydro-6-hydroxy-methylpurine ribonucleoside, results in a lowering of its affinity for the enzyme by several orders of magnitude. The synthesis of the analogue and related compounds is described, and their properties compared with those of other photoadducts and of the naturally occurring inhibitors covidarabine and coformycin. Binding of these inhibitors is found to result in the appearance of ultraviolet-absorbing bands in the neighborhood of 323 nm.

Order–disorder transitions in substituted adamantanes

Abstract: Order–disorder transitions in 1- and 2-methyladamantane, 1,3-dimethyladamantane, 1,3,5-trimethyladamantane, 1,3,5,7-tetramethyladamantane and in the 1-halogenoadamantanes have been investigated by differential scanning calorimetry. The effects of substituent groups on the disordered phase behaviour of these molecules are discussed.

Color photographic processing method

Abstract: A method for processing a silver halide color photographic light-sensitive material which comprises developing an image-wise exposed silver halide color light-sensitive material in the presence of (a) an aromatic primary amine color developing agent, (b) hydroxylamine or a hydroxylamine derivative, and (c) a 1-aryl-3-pyrazolidone derivative containing two substituent groups at the 4-position thereof.

1,2,3-Thiadiazole amides

Abstract: A series of novel 4-amino-2-(thiadiazole-carbonyl piperazinyl)-6,7-dimethoxyquinazolines is disclosed having antihypertensive properties. The thiadiazole substituent may be optionally substituted with alkyl or lower alkoxy carbonylamino groups. A representative embodiment of the invention is 4-amino-6,7-dimethoxy-2-[4-(5-ethoxy-carbonylamino-1,2,3-thiadiazole-4-carbonyl)-piperazin-1-yl]-quinazoline.

Ab initio calculations on 4-substituted styrenes: a theoretical model for the separation and evaluation of field and resonance substituent parameters

Abstract: Ab initio (STO-3G minimal basis set) molecular orbital calculations on 4-substituted styrenes and CH3X–C2H4 pairs indicate that ΔqH (the charge density difference between β-vinyl protons) provides a direct theoretical measure of the field effect of a polar substituent. Σqcπ, the total substituent-induced π electron density change in styrene provides a theoretical measure of the resonance effect of the substituent. ΔqH and Σqcπ provide the basis of a theoretical dual substituent parameter scale, TF and TR0. This scale compares very closely with experimental DSP scales, indicating the latter scales are fundamentally valid. The calculations also indicate that field effects and σ inductive effects do not show parallel trends. It is concluded that field effects are more important than σ inductive effects except at very close range. Individual carbon π electron densities reflect both resonances effects and polar π inductive effects.

Derivatives of 4-aminopiperidine as stabilizers for polymers

Abstract: Derivatives of sterically hindered 4-aminopiperidines are effective as light-stabilizers for organic polymers, especially for polyolefins. The piperidine ring is substituted with at least five alkyl groups, preferably methyl and ethyl groups. The 4-amino group is substituted with mono- or divalent acyl groups. The nitrogen in 1-position may also be substituted with a monovalent organic substituent. The compounds can be synthesized starting from higher homologs of acetone in sequence of several reaction steps.

Fluorination with substituted (difluoroiodo)arenes.

Abstract: The reaction of substituted (difluoroiodo)arenes with 1-phenyl-1-(m-chlorophenyl)ethylene results in 1,1-difluoro-1-(m-chlorophenyl)2-phenylethane, with 1-phenyl-1-(p-methoxyphenyl)ethylene in 1,1-difluoro-1-phenyl-2-(p-methoxyphenyl) ethane, and with 1-phenylcyclopentene and 1-phenylcyclohexene in rearranged gem-difluoro compounds. The reaction with norbornene results in three products: fluoronortricyclane (9–12%), 2-exo-7-syn-difluoronorbornane (75–86%), and 2-exo-7-anti-difluoronorbornane (5–15%) depending upon the substituent on the phenyl ring in (difluoroiodo)arenes.

13C, 13C coupling constants and 13C chemical shifts of aromatic carbonyl compounds. Effects of ortho‐ and peri‐interactions involving the carbonyl substituent

Abstract: Carbon-13 n.m.r. data have been determined for a series of 26 aromatic carbonyl compounds including benzoyl, naphthoyl and pyrenoyl derivatives 13C labelled in the carbonyl group. Doubly labelled anthraquinone has also been included. The compounds investigated comprise non-hindered molecules and molecules in which the carbonyl substituent is subject to ortho- or peri-interactions affecting conjugation of the carbonyl group with the aromatic ring. The dependence of long range 13C,13C coupling constants involving the carbonyl carbon, in particular 2J and 3J, on steric conditions is discussed, as is the possibility of deciding on the orientation of the carbonyl bond. The following results have emerged. 2J(s-t)>2J(s-c) for ketones and aldehydes, and the reverse is valid for acids and acid derivatives. (s-t and s-c refer to the orientation of the CO group relative to the aromatic bond in question with respect to the connecting single bond). For ketones 3J(t,s-c) 3J(c) and 3J(t)>2J, confirming earlier results. Theoretical calculations on a few model compounds are qualitatively in accordance with the experimental results. Some sign determinations for coupling constants are presented. A short discussion is given of substituent effects on chemical shifts. Observed trends are consistent with earlier results.

The dimerization of 1‐alkynes by rhodium(I) catalysts. Effect of phosphorus ligands on regioselectivity

Abstract: The dimerization of 1-alkynes by rhodium(I) complexes in the presence of phosphorus ligands is described. The products are linear and branched dimers, the ratio of which is correlated with the electronic parameters, vCO of Ni(CO)3L, of the ligands L, but no simple correlation is apparent between their steric parameter and the selectivity. Electron-donating ligands promote the formation of the linear dimer. The substituents of the 1-alkynes also affect the distribution of linear and branched dimers. Electron-donating substituents prefer linear isomer to branched one. The reactivity of the substituted 1-alkynes (RCCH) increased with substituent R in the order

Substituent constants for correlation analysis

Abstract: Constants for pi and omega ahve been measured for a miscellaneous group of aromatic substituents of interest to medicinal chemists. Swain and Lupton's gamma and kappa values have been calculated from the omego constants. Values for molar refractivity are also given for each of the substituents.

The Effect of Dye Structure on Order Parameter in a Nematic Liquid Crystalline Host1

Abstract: The order parameters (S) of a number of substituted azobenzenes and phenylazothiazole, -benzothiazole and -heterocyclic compounds dissolved in a nematic liquid crystalline host have been determined. The measured order parameters for a class of azo compounds bear a strong relationship to the structure of the dye. For azobenzenes, there is an additivity of substituent effects which leads to good agreement between empirically-derived and observed S values. Disazo dyes give higher S values than the corresponding monoazo dyes. For heterocyclic phenylazo dyes, the end group substituents on the phenyl ring play a significant role in influencing S, whereas the nature of the heterocyclic system, as well as the end group substituents on the heterocyclic ring, are only of minor importance. The presence of an N-H moiety as part of a heterocyclic ring, or the fusion of a benzene ring onto a heterocyclic ring, can lead to significant changes in the order parameter.

Photoelectron spectra of substituted oxiranes and thiiranes. Substituent effects on ionization potentials involving σ orbitals

Abstract: The state assignments corresponding to the second and third ionization potentials of oxirane have been the subject of some uncertainty due to the great sensitivity of Koopmans' theorem predictions to the type of calculation performed for this molecule In this study, the assignments made by Basch et al for oxirane are confirmed through measurement of the photoelectron spectra of methyl-, 1,1-dimethyl-, 1,2-dimethyl, ethyl-, vinyl-, phenyl-, chloromethyl-, and fluoromethyloxirane The second and third ionizations of thiirane are confirmed to be of the opposite order from those in oxirane by correlations of these values with those reported here for methyl-, vinyl, and methoxymethylthiiraneIn these compounds, mono-substitution by alkyl groups causes a decrease in ionization potential not obviously related in a simple way to the type of orbital involved Thus, assignments cannot be made straightforwardly by observing ionization potential changes caused by hyper-conjugating or inductive substituents Alkyl g

Stabilization of synthetic polymers by penta-or-hexa-substituted 4-piperidinol derivatives

Abstract: Polymers, both natural and synthetic, are stabilized against the deterioration resulting from heat and/or light by the incorporation of certain 2,2,6,6-tetra-substituted-4-piperidinol derivatives which additionally have an alkyl, alkenyl, alkynyl or aralkyl substituent at one or both of the 3- and 5- positions.